The new video coding standard, H.265/HEVC, as described in B. Bross, W. J. Han, J. R. Ohm, G. J. Sullivan, Y. K. Wang and T. Wiegand, “High Efficiency Video Coding (HEVC) Text Specification Draft 10”, document JCTVC-L1003, ITU-T/ISO/IEC Joint Collaborative Team on Video Coding (JCT-VC), January 20 and G. J. Sullivan, J. R. Ohm, W. J. Han and T. Wiegand, “Overview of the High Efficiency Video Coding (HEVC) Standard”, IEEE Transactions on Circuits and Systems for Video Technology, Vol. 22, No. 12, December 2012, herein after Sullivan, can reduce the bit rate by half relative to H.264/AVC for the same visual quality. HEVC, like previous video coding standards, is a hybrid video coding scheme that uses improved features in all encoding modules to enhance the coding efficiency. In intra coding, compared to H.264's 9 modes, HEVC employs 33 directional modes for angular prediction in addition to DC and planar modes as described in J. Lainema, F. Bossen, W. J. Han, J. Min and K. Ugur, “Intra Coding of the HEVC Standard”, IEEE Transactions on Circuits and Systems for Video Technology, Vol. 22, No. 12, December 2012, herein after Lainema. This number of modes is now adequate to more precisely predict the directional patterns in high-resolution videos when large block sizes are used. However, this, in addition to the transform tree optimization, has rendered the HEVC intra coding operation much more complex, as compared to previous video codecs.
In mode decision, many computations are needed to select the best intra mode by performing a highly demanding rate distortion optimization (RDO) process. To address this problem, during the development of the standard and after its finalization, several research studies have proposed various approaches for fast intra mode decision.
In Piao et al., Y. Piao, J. H. Min and J. Chen, “Encoder Improvement of Unified Intraprediction”, JCTVC-C207, Guangzhou, China, October 2010, authors have proposed rough mode decision (RMD) as a step prior to RDO to exclude the majority of modes from the highly expensive RDO. Their approach reduces the encoding time by about 50%, and has been used in a HEVC reference implementation since its early versions.
Zhao et al., L. Zhao, L. Zhang, X. Zhao, W. Ma, D. Zhao and W. Gao, “Further Encoder Improvement of Intra Mode Decision”, JCTVC-D283, Daegu, Korea, January 2011, herein after Zhao, has further reduced the number of candidates by introducing the concept of most probable modes (MPM). They achieved time savings of up to 28% using HM 0.9 with almost equivalent rate-distortion performance. The HEVC reference implementation HM (Test Model) 4.0 and the versions following it include Zhao's approach.
In Jiang et al., W. Jiang, H. Ma, Y. Chen, “Gradient Based Fast Mode Decision Algorithm for Intra Prediction in HEVC”, CECNet, April 2012, has proposed a fast mode decision approach based on the gradient information of pixels and obtained another 20% time reduction in comparison with HM 4.0.
Chen et al., G. Chen, Z. Pei, L. Sun, Z. Liu and T. Ikenaga, “Fast Intra Prediction for HEVC based on Pixel Gradient Statistics and Mode Refinement”, ChinaSIP, Beijing, July 2013, herein after Chen, has improved the gradient method by introducing a mode decision approach based on pixel gradient statistics and mode refinement. They applied this to HM 8.0 and achieved a 28% time reduction.
Recently, Zhang et al., H. Zhang and Z. Ma, “Fast Intra Mode Decision for High Efficiency Video Coding (HEVC)”, IEEE Transactions on Circuits and Systems for Video Technology, Vol. 24, No. 4, April 2014, has proposed a method for fast intra coding and achieved significant time reduction by using the Hadamard cost-based progressive rough mode search and early coding unit split termination.
The same is applicable for by Zhao et al., L. Zhao, X. Fan, S. Ma, D. Zhao, “Fast Intra Encoding Algorithm for High Efficiency Video Coding”, Signal Processing: Image Communication 29, June 2014, pages 935-944, who has proposed to reduce time consumption by excluding some coding unit and transform unit depths.
Thus, existing improvements on coding performance in HEVC video codec have been achieved at the expense of higher computation complexity in both inter and intra coding.
Therefore, it would be beneficial to provide a method and system for HEVC intra coding operation that would be less complex and more time efficient.